The present invention is related to an automatic transmission and, in particular, to the input shaft and stator support shaft of an automatic transmission.
In a typical automatic transmission, such as for instance, a General Motors Powerglide transmission, a power input shaft 10 (see FIG. 1 (PRIOR ART)) includes an oil gallery 12 running axially through an interior of the input shaft 10 which is part of the oil management system of the transmission. The input shaft is positioned to rotate within an internal axial bore 22 of the stator support shaft 20. The input shaft includes a generally radial oil flow bore 14 connecting an exterior of the input shaft to the input shaft oil gallery 12. To provide control of the oil flow between the stator support shaft and the input shaft, it is necessary to provide two oil seals 16 and 18 between the input shaft 10 and the stator support shaft 20, positioned axially forward and rearward of the input shaft oil flow bore 14, respectively. The oil seals 16 and 18 are generally in the form of split metal rings so that they can be expanded to install over larger diameter portions of the input shaft 10.
The stator support shaft 20 includes two axially separated generally radial oil flow bores 24 and 26 connecting an exterior of the stator support shaft 20 to the internal axial bore 22 of the stator support shaft 20. The forward stator support shaft oil flow bore 24 is positioned axially forward of the forward input shaft oil seal 16 and the rearward stator support shaft oil flow bore 26 is positioned axially between the forward input shaft oil seal 16 and rearward input shaft oil seal 18 to be in generally axial alignment with the input shaft oil flow bore 14. 
The oil flow is as follows. Hot oil flows from the torque converter 36 in the forward chamber 38 created between the stator support shaft 20 and the input shaft 10 to be blocked by the forward oil seal 16 and forced through the forward stator support shaft oil flow bore 24 to the oil cooler 30. The oil is then returned from the oil cooler 30 to the rearward stator support shaft oil flow bore 26 and into the chamber 40 created between the stator support shaft 20, the input shaft 10 and the two oil seals 16 and 18. The oil is then forced through the input shaft oil flow bore 14 to the input shaft oil gallery 12 where it can then be directed to further oil flow bores in the input shaft for cooling and lubrication of the direct clutches, the planetary gear set, the rear thrust washer and the input shaft pilot bushing. Each of the oil flow bores is critically sized to provide a desired downstream restriction to the oil flow and maintain the desired operating oil pressure in the torque converter for proper operation of the transmission.
In a standard Powerglide transmission, the oil seals 16 and 18 are positioned in circumferential oil seal grooves 32 and 34, respectively, cut into the exterior of the input shaft 10 on each side of the input shaft oil flow bore 14. Each oil seal groove 32, 34 then receives an oil seal 16, 18 that engages the internal axial bore 22 of the stator support shaft 20 to provide a sealing engagement between the input shaft 10 and the stator support shaft 20. The input shaft 10 includes turbine splines 42 at a forward end for engaging the turbine of the torque converter 36. The stator support shaft 20 includes stator splines 42 at a forward end for engaging the stator of the torque converter 36 and stator support splines at a central portion for engaging the stator support and preventing rotation of the stator support shaft 20.
Such a transmission has disadvantages however. The General Motors Powerglide transmission was originally developed for vehicles generally producing significantly less than 300 horsepower. Although no longer in original equipment production, the Powerglide  transmission is now one of the most popular automatic transmissions used in drag racing vehicles. The power that these vehicles produce is often well in excess of 500 horsepower and can be in excess of 1500 horsepower. The additional torque produced by the engines of these vehicles is compounded by the fact that the torque converter 36 multiplies the torque of the engine, generally by as much as a factor of two or more, under low speed/high engine torque output conditions. Thus, this additional torque and power, coupled with the increased traction resulting from large, modern drag racing tires, places stresses on the transmission that were never envisioned in the original design.
As a result, the input shaft 10 has become a weak link in the transmission. In particular, the circumferential input shaft oil seal grooves 32 and 34 for receiving the oil seals 16 and 18 not only decrease the cross-sectional area and strength of the input shaft 10, they also create stress risers that can hasten input shaft failure such that input shaft breakage at one of the circumferential oil seal grooves has become commonplace in such transmissions used in high horsepower drag racing vehicles.
One approach to this input shaft breakage problem has been to forego the circumferential oil seal grooves and oil seals between the input shaft and the stator support shaft. This reduces power input shaft breakage but also reduces control of the oil flow with significant undesirable effects. For instance, since the oil is not properly routed as discussed above, torque converter discharge oil is allowed to enter the front of the transmission and is not effectively routed to the oil cooler and then to specific areas of the transmission for cooling and lubrication. Further, because of the loss of the restrictions in the oil flow caused by the sized oil flow bores in the standard Powerglide transmission, the torque converter internal oil pressure cannot be effectively maintained for proper operation. 
Another approach to the shaft breakage problem has been to increase the diameter of at least a portion of the input shaft 10 to minimize or eliminate the cross-sectional area reduction of the shaft, as compared to a standard shaft, caused by the circumferential oil seal grooves 32, 34. However, such an approach requires that other non-standard components be used to accommodate the increased size of the input shaft. For instance, the stator support shaft in such a transmission must have a larger diameter internal axial bore to accommodate the increased input shaft size and larger oil sealing rings. In addition to requiring such additional custom components at increased cost, the wall thickness of the stator support shaft is decreased by the larger internal axial bore, thereby compromising the strength of the stator support shaft. Further, the stress risers created by the oil seal grooves may not be completely eliminated by the increase in the input shaft diameter.
It is an object of the present invention to provide an automatic transmission that overcomes the above disadvantages.
It is a further object of the present invention to provide an automatic transmission having increased power handling capabilities.
It is a further object of the present invention to provide an automatic transmission having increased power handling capabilities while maintaining proper oil flow in the transmission.
It is a further object of the present invention to provide an input shaft for an automatic transmission that is stronger than a standard input shaft while retaining the proper oil flow in the transmission.
It is a further object of the present invention to provide an input shaft for an automatic transmission having an increased diameter for additional strength without eliminating oil control seals between the input shaft and the stator support shaft. 